An events-first approach has been successfully used for many years in Williams College introductory CS courses, where beginners program responses to mouse events in graphics programs during their very first week [3,4,5]. Java libraries hide complexities of the Java event model, whose details are revealed as these courses progress towards traditional Java GUI programming. App Inventor extends this events-first approach by providing primitive event-handler blocks for all types of events that can occur on a mobile device, enabling CS0 students to program responses to general GUI events, sensor events (e.g. device shaking), and social events (e.g., incoming texts) on their very first day. This expands the range of apps students can build and increases their motivation.